Control system



A. L. HARVEY.

CONTROL SYSTEM. APPLICATION FILED MAY I5. 1919.

Patented Aug. 15, 1922.

WITNESSES:

. INVENTOR {J 7 i A/berf L. flan 6y %W BY MM ATTORNEY PATENT. OFFICE.

ALBERT L. HARVEY, OF 'WILKINSBURG, PENNSYLVANIA, ASSIGNOR TO WESTING- HOUSE ELECTRIC & MANUFACTURING VANIA.

COMPANY, A CORPORATION OF PENNSYL- CONTROL SYSTEM.

Application filed May 15,

T 0 all to [1.0m it may concern:

Be it known that I. ALBERT L. HARVEY, a citizen of the United States, and a resident of lVilkinsburg, in the county of Allegheny and State of Pennsylvania, have invented a new and useful Improvement in Control Systems, of which the following is a specification;

My invention relates to motorcontrol systems and particularly to systems for controlling shunt and compoundewound direct current motors that are provided with means for dynamic braking.

The object of my invention is to provide an improved system for controlling the shunt-field excitation of motors of the above-designated character.

In a system arranged according to my invention, the resistor that is in series with the shunt field-magnet winding is controlled by a relay that is energized in accordance with the voltage drop across both the accelerating and the dynamic-braking resistors. 'The relay may be provided with a coil connected across both the accelerating and the dynamic-braking resistors or with separate coils that are respectively connected across these two resistors. A

. strongly excited field is thus provided during both the accelerating and the dynamicbraking periods.

In the accompanying drawings, Figure 1 is a diagrammatic view of circuits and apparatus embodying my invention as applied to a unidirectional, compound-wound motor; Fig. 2 is a similar view of my invention as applied to a reversing motor; Fig.

3 is a schematic view of the system of Fig.

2, and Fig. 4 is a schematic view of a modification.

In the system of Fig. 1, a motor, having an armature 1, a shunt field-magnet winding 2 and a series field-magnet winding 3, is adapted to be supplied from any suitable source of energy byline conductors 4 and 5 and a line knife switch 6. An accelerating resistor '7 is connected in series with the armature 1 and is adapted to be short-circuited by a contactor 8 having a coil 9 that is adapted to be connected across the terminals of the armature. The circuit of the motor may be closed by a line contactor 10, having an actuating coil 11, the circuit of which may be closed by a start push-button switch and opened by a stop push-button Specification of Letters Patent.

Patented. Aug. 15, 1922.

1919. Serial No. 297,357.

switch. A pair of switches 12 and 13 are mechanically connected to the contactor 10, the former of which creates a holding circuit, independent of the start push-button switch, for the coil 11 and controls the circuit of the coil 9, and the latter of which, the switch 13, is adapted to control a dynamic-braking circuit for the motor, comprising a dynamic-braking resistor 14 and a coil 15 for maintaining the contactor '10 open and the switch 13 closed. An. overload relay 16 is provided with a coil 17 In circuit with the shunt] field-magnet winding 2 is a resistor 18 that is adapted to be short-circuited by a relay 19 having an actuating coil 20 that is connected across both the resistors 7 and 14 in series.

In operation, assuming that the line knife switch 6 is closed and that the start pushbutton switch is depressed, a circuitis established from the line conductor 4, through the knife switch 6, the coil 17, the overload relay 16, the start and stop push-button switches, the actuating coil 11, the series field-magnet winding 3 and the knife switch 6 to the line conductor 5. The contactor 10 is thereupon closed by its actuating coil 11 simultaneously with the closing of the switch 12 and the opening of the switch 13. The start push-button switch may be thereupon released, a holding circuit for the coil 11 being established from the line conductor 4, through the knife switch 6, the coil 17, the overload relay 16, the switch 12, the stop push-button switch, the coil 11, the series field-magnet winding 3 and the knife switch 6, to the line conductor 5. The contactor' 10 will be maintained closed by its coil 11 until such time as the above-traced circuit is opened by the stop push-button switch or the overload relay 16.

The closing of the contactor 10 establishes the motor circuit from the line conductor 4, through the knife switch .6, the coil 17, the contactor 10, the armature 1, the accelerating resistor 7, the series field-magnet winding 3 and the knife switch 6, to-the line conductor 5. The coil 20 becomes thereupon energized, in accordance with the voltage drop across the resistor 7 (the circuit, traced below, of the resistor 14 beingopen at the switch 13), thereby effecting the 010s ing of the relay 19 to effect the short-circuiting of the resistor 18. .The circuit of the. shunt field-magnet- Winding 2 willnow extend from the line conductor 4, through the knife switch 6, the coil 17, the relay 19, the shunt field-magnet winding 2 and the knife switch 6, to the line conductor 5. The shunt field-magnet winding 2 is thus strongly excited during the accelerating o1 eration of the motor 1.

The coil 9 is connected across the armature 1 in a circuit extending from one brush through the coil 9, the switch 12-, the overload relay 16, and the contactor 10, to the other brush of the armature 1. When the counter-electron'iotive force of the motor attains a predetermined value, therefore, the contactor 8 will be closed by its coil 9 to effect the short-circuiting of the resistor 7. The motor will then operate at a prede termined speed.

Upon the short-circuiting of the resistor 7, the coil 20 becomes de-energized, effecting the opening of the relay 19 by gravity. The circuit of the shunt field-magnet winding 2 then extends from the line conductor 4, through the knife switch (5, the coil 17, the resistor 18, the shunt field-magnet winding 2 and the knife switch 2, to the line conductor 5. That is, the resistor. 18 becomes inserted into the circuit of the shunt fieldmagnet. winding 2 to Weaken the excitation of this winding and to effect the operation of the motor at its maximum speed.

\Vhen it is desired to stop the motor, the stop push-button switch may be actuated to break the circuit of the coil 11. The contactor l0 thereupon drops open by gravity, cf fecting the opening also of the switch 12 and the closing of the switch 13. The motor then acts as generator, a dynamic-braking circuit being established the armature 1, through the switch 13, the coil 15, which aids gravity in maintaining the swltch 13 closed, and the dynamic-braking resist-or 1 1, to the other brush of the armature 1. The motor continues to act as a generator until it comes approximately to rest. During all this time, the coil 2 0 is energized in accordance with the drop 11 voltage across the resistor 14, s. that the relay 19 is maintained closed to effect the short-circuiting of the resistor 18 and to provide for a strongly excited shunt fieldinagnet winding during the dynamic-braking operation.

In accordance with my invention, therefore, the relay 19 is maintained closed duringboth the accelerating and the dynamicbraking operations to effect the short-ciroulting of the resistor 18 and the consequent strong excitation of the field-111agnet windmg 2. The motor is thus provided with a strongly excited field during both the accelerating and the dynamic-braking operations. I

The system of Fig. 2 differs somewhat from that of Fig. 1. As the III lZQ I 9i i from one brush of system is designed for operation in two directions, it is provided with not simply one contactor 10 but two, numbered 10 and (it), having actuating coils 11 and 61, respectively, and coils 15 and 65, respectively. The contactors 10 and (30 are provided with mechanically connected contactors 12 and G2 and switches 13 and 63, respectively. The relay 19 is provided, in this instance, with two coils 20 and that are respectively connected across the resistors 7 and 14. An additional master switch 71 is provided, having two positions in each of two opposite directions of operation, in one of which it controls the coil 11 and a coil 72, of an additional line contactor 73, and in the other of which it controls the coils 61 and 72. A switch 74 is mechanically connected to the line contactor 73 and controls the circuit of the c0unterelectrom0tive force coil 9. The resistor 7 is adapted to be short-circuiteal in two steps, one of which is controlled by a contactor 75 having a series coil 76. This contactor and its coil are omitted from the system of Fi 1 in order to simplify the drawings of that system. The master switch 71 is connected to the line conductor 4.

Upon the actuation of the master switch 71 to its first position toward the left, a circuit is established from the line conductor 4, throu h the master switch 71, the coil 11 and the knife switch (3, to the line conductor 5. The contactor-s 10 and 12 are thereupon closed. and the switch 13 is thereupon opened by the coil 11. The circuit of the motor is, nevertheless, maintained open at the contactor 73. Upon the master switch 71 bein actuated to its second position toward the left, a circuit becomes established from the line conductor 4, through the master switch 71, the coil 72 and the knife switch 6, to the line conductor 5.

The motor circuit then extends from the line conductor 4, through the contactor 10, the armature 1, the switch 12, the coil 76, the resistor 7, the series field-magnet winding 2-3, the line contactor 73 and the knife switch 6, to the line conductor 5. The coil 20, becoming energized by the drop in voltage across the resistor 7, the relay 19 becomes closed to effect the short-circuitin of the resistor '18. The circuit of the shunt fieldmagnet winding 2, accordingly, extends from the line conductor 1, through the" relay 19, the shunt field-magnet winding 2 and the knife switch 6, to the line conductor The shunt field-magnet winding 2 is thus strongly energized during the accelerating operation.

The contactor 75, which is preferably of the lookout type, will become closed by its coil 76 upon the motor current dropping to a predetermined value to effect the short-circuiting of a portion of the resistor 7.- After a time, when the counter-electromotive force attains a predetermined value, the coil 9 will effect the closing of the contactor 8 to affect the short-circuiting of the remaining portion of the resistor 7. The cir- I cuit of the coil 9 extends from one terminal winding circuit. The motor will thereupon operate at maximum speed.

To stop the motor, the master switch 71 may be returned to its initialillustrated position. This will have the effect of opening the control circuits, so that the motor will become disconnected from the line conductors 4 and 5. Simultaneously with the opening of the contactor 10., the switch 13 will become closed, so that a dynamicbraking circuit will be established for the motor which will extend from one brush of the armature 1 through the switch 13, the coil 15, the resistor 14, the coil 65 and the switch 63, to the other brush of the armature 1. The resistor 14:, becoming thus energized, the coil 70, which is connected across its terminals, will effect the closing of the relay 19 and the consequent shortcircuiting of the resistor 18 in order to permit of the field-magnet winding2 being strongly excited. A strong field is thus provided for the 'motor during dynamic braking. a

To operate the motor in the reverse direction, the master switch 71 may be actuated to the right. The coil 61 will become energized to efiect the closing of the contactors 60 and 62, which will establish the motor circuit for operation in the reverse direction. The operation is substantially the same as that described above in connection with the description of the operation following upon the closing of the contactors 10 and 12. The coil 20 is connected across the resistor 7 to maintain the relay 19 closed during acceleration, and the coil operates, during dynamic-braking, to efiect a similar result during braking.

The circuits of Fig. 2 are schematically shown in Fig. 3. It will be noted that the reason for employing two coils 20 and 70.. instead of a single coil 20, as in the system,

of Fig. 1, is that the contactors 12 and 60 are connected in circuit between the armature land the resistor 7. If the resistor 7 be permanently connected to the armature 1, and if the resistor 14 be connected between the two, as in Fig. 4, a single coil 20 may be employed, as in the case of the system of Fig. 1. In the system of Fig. 4, the contactors 10 and 12 and the switch 13 are mechanically connected, as in the system of Fig. 2. The contactors 60 and 62. are also mechanically connected but the switch 63 is omitted. If the switch 63 were not omitted, it would be necessary to employ two coils 20 and 70, as in the system of F ii. 2.

lthough I have shown several systems embodying my invention, it will be clear that the invention is not restricted thereto and I desire that it be construed broadly, as defined in the appended claims.

I claim as my invention:

1. The combination with an electric motor having a pair of accelerating resistors and a dynamic-braking resistor, of means responsive to the drop in potential across one of said accelerating resistors and said dynamic-braking resistor for controlllng the other of said accelerating resistors.

2. The combination with an electric motor having armature and field-magnet windings, resistors in series therewith and a resistor in parallel to said armature winding, of a switch for controlling said field resistor having an energizing coil connected across said other resistors.

3. The, combination with an electric motor having armature and field-magnet windings, resistors in series therewith and a resistor in parallel to said armature winding, of a switch for controlling said field resistor having an energizing coil responslve to the drop in potential connected across said parallel connected resistor.

4. The combination with an electric motor having armature andshunt fieldmagnet windings, resistors in series therewith, a resistor in parallel to said armature ALBERT L. HARVEY. 

